SANSKAR'S OG PROBLEMS

Revision as of 21:03, 28 January 2024 by Ddk001 (talk | contribs) (Problem1)

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Problem 1

Let $\overline{ab}$ be a 2-digit positive integer satisfying $\overline{ab}^2=a! +b!$. Find $a+b$ .

Solution 1 by ddk001 (Casework)

Case 1: $a>b$ In this case, we have \[\overline{ab}^2=a! +b!=(1+a \cdot (a-1) \cdot \dots \cdot (b+1)) \cdot b! \implies b!|\overline{ab}^2=(10a+b)^2\]. If

Problem2

For any positive integer $n$, $n$>1 can $n!$ be a perfect square? If yes, give one such $n$. If no, then prove it.